Modifying agent, method for producing modified conjugated diene polymer using modifying agent, and modified conjugated diene polymer

ABSTRACT

Provided are a modifying agent obtained by subjecting a silicon-containing compound having a protected primary amino group and at least two hydrolyzable groups to complete condensation, a method of producing a modified conjugated diene-based polymer, a modified conjugated diene-based polymer obtained by the production method, a rubber composition using the polymer, and a pneumatic tire. The modified conjugated diene-based polymer has excellent low heat generating property and abrasion resistance, and the rubber composition is obtained by using the modified conjugated diene-based polymer and the pneumatic tire is obtained by using the rubber composition.

TECHNICAL FIELD

The present invention relates to a modifying agent, a method ofproducing a modified conjugated diene-based polymer using the modifyingagent, and the modified conjugated diene-based polymer, and a rubbercomposition using the polymer and a pneumatic tire using the rubbercomposition.

BACKGROUND ART

A large number of technologies concerning a modified rubber for a rubbercomposition using silica or carbon black as a filler have beenconventionally developed in order that a rubber composition having lowheat generating property may be obtained. Of those, in particular, thefollowing method has been proposed as an effective method (see, forexample, Patent Literature 1 or 2). A polymerization active site of aconjugated diene-based polymer obtained by anionic polymerizationinvolving using an organic lithium is modified with an alkoxysilanederivative containing a functional group that interacts with a filler.

Compounding a reinforcing filler into a rubber composition using amodified polymer obtained by the production method can secure low heatgenerating property. However, abrasion resistance when silica is appliedto the reinforcing filler has still been insufficient.

In recent years, however, a request for a reduction in the fuelconsumption of an automobile has started to become more and morestringent in relation to a social demand for energy savings and a globaltrend toward carbon dioxide emission control in association with thegrowth of interests in environmental problems. Accordingly, there havebeen growing requests for improvements in the low heat generatingproperty and abrasion resistance of a rubber composition, and henceadditional development has been requested.

CITATION LIST Patent Literature

[PTL 1] JP 06-57767 B

[PTL 2] WO 03/029299 A1

SUMMARY OF INVENTION Technical Problem

In view of such circumstances, a problem to be solved by the presentinvention is to provide a modifying agent with which a modifiedconjugated diene-based polymer excellent in low heat generating propertyand abrasion resistance can be obtained, and an object of the presentinvention is to provide a modified conjugated diene-based polymer usingthe modifying agent, a rubber composition using the polymer, and apneumatic tire using the rubber composition.

Solution to Problem

The inventors of the present invention have made extensive studies toachieve the object, and as a result, have found that the object can beachieved by using a modifying agent obtained by condensing asilicon-containing compound having a specific amino group that isprotected and a specific hydrolyzable group. The present invention hasbeen completed on the basis of such finding.

That is, the present invention provides:

(1) a modifying agent obtained by subjecting a silicon-containingcompound having a protected primary amino group and at least twohydrolyzable groups to complete condensation;(2) a method of producing a modified conjugated diene-based polymer,comprising: a modifying step of causing the modifying agent according tothe above-mentioned item (1) to react with an active site of aconjugated diene-based polymer having the active site to modify thepolymer; and a deprotecting step to be performed after completion of themodifying step;(3) a modified conjugated diene-based polymer obtained by the productionmethod according to the above-mentioned item (2);(4) a rubber composition, comprising the modified conjugated diene-basedpolymer according to the above-mentioned item (3); and(5) a pneumatic tire obtained by using the rubber composition accordingto the above-mentioned item (4).

Advantageous Effects of the Invention

According to the present invention, there can be provided a modifiedconjugated diene-based polymer excellent in low heat generating propertyand abrasion resistance, a rubber composition using the modifiedconjugated diene-based polymer, and a pneumatic tire using the rubbercomposition.

In addition, according to the present invention, there can be provided amodified conjugated diene-based polymer that does not generate anyvolatile organic compound (VOC).

DESCRIPTION OF EMBODIMENTS

A modifying agent of the present invention is characterized by beingobtained by subjecting a silicon-containing compound having a protectedprimary amino group and at least two hydrolyzable groups to completecondensation.

The hydrolyzable groups are each preferably a hydrolyzable group thatforms a silanol group together with at least two silicon atoms byhydrolysis. Here, the term “complete condensation” means that allmonomers of the silicon-containing compound in the modifying agent arecondensed and hence no monomer of the silicon-containing compound existsin the modifying agent. The silicon-containing compound needs to have atleast two hydrolyzable groups each of which forms a silanol grouptogether with a silicon atom in order that the silicon-containingcompound may be hydrolyzed and completely condensed.

The modifying agent of the present invention may be obtained by thecondensation of compounds of the same kind, or may be obtained by thecondensation of two or more kinds of dissimilar compounds.

Each of the hydrolyzable functional groups is a functional group capableof chemically reacting with an active site of a conjugated diene-basedpolymer, and is preferably a hydrocarbyloxy group or a halogen atom,more preferably a group selected from the group consisting of an alkoxygroup having 1 to 12 carbon atoms, a phenoxy group and a benzyloxygroup, or a halogen atom, still more preferably an alkoxy group having 1to 20 carbon atoms, particularly preferably an alkoxy group having 1 to12 carbon atoms. A methoxy group, an ethoxy group, a propyloxy group, anisopropyloxy group, an n-butoxy group, and a tert-butoxy group can begiven as specific examples of the alkoxy group having 1 to 20 carbonatoms. The halogen atom is preferably a chlorine atom, a bromine atom,or a fluorine atom.

The modifying agent of the present invention is preferably a compoundrepresented by the following general formula (1) or (2).

(In the formula, R¹ and R² each represent a divalent aliphatichydrocarbon group having 1 to 20 carbon atoms, a divalent aromatichydrocarbon group having 6 to 18 carbon atoms, or a single bond, and maybe identical to or different from each other, R³, R⁴, and R⁵ eachrepresent a monovalent aliphatic hydrocarbon group having 1 to 20 carbonatoms or a monovalent aromatic hydrocarbon group having 6 to 18 carbonatoms, and may be identical to or different from one another, A¹represents a group for bonding the modifying agent and a conjugateddiene-based polymer by adding to, or substituting for, an active site ofthe conjugated diene-based polymer, B¹ represents a primary amino groupprotected with a hydrolyzable protective group, a+b+c=2, a represents 1to 2, b represents 0 to 1, and n represents 2 to 20.)

(In the formula, R⁶, R⁸, and R¹¹ each represent a divalent aliphatichydrocarbon group having 1 to 20 carbon atoms, a divalent aromatichydrocarbon group having 6 to 18 carbon atoms, or a single bond, and maybe identical to or different from each other, R⁷, R⁹, R¹⁰, R¹², and R¹³each represent a monovalent aliphatic hydrocarbon group having 1 to 20carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 18carbon atoms, and may be identical to or different from one another, A²represents a group for bonding the modifying agent and a conjugateddiene-based polymer by adding to, or substituting for, an active site ofthe conjugated diene-based polymer, B² represents a primary amino groupprotected with a hydrolyzable protective group, B³ represents a linear,branched, alicyclic, or aromatic, monovalent hydrocarbon group having 1to 30 carbon atoms and having a functional group selected from the groupconsisting of an isocyanate group, a thioisocyanate group, an imineresidue, an amide group, a cyclic secondary amino group, an onium saltresidue of a cyclic secondary amine, a non-cyclic secondary amino group,an onium salt residue of a non-cyclic secondary amine, an isocyanuricacid triester residue, a cyclic tertiary amino group, anon-cyclictertiary amino group, a nitrile group, a pyridine residue, an onium saltresidue of a cyclic tertiary amine, and an onium salt residue of anon-cyclic tertiary amine, or a linear, branched, alicyclic, oraromatic, monovalent hydrocarbon group having 1 to 30 carbon atoms whichmay contain at least one kind of heteroatom selected from an oxygenatom, a sulfur atom, and a phosphorus atom, a1+b1+c1=2, a1 represents 1to 2, b1 represents 0 to 1, a2+b2+c2=2, a2, b2, and c2 each represent 0to 2, and p and q each independently represent 1 to 10.)

The general formula (2) is represented as A²-R⁶—X_(p)—Y_(q)—R⁷ when Xand Y are defined as represented by the following general formulae (2a)and (2b). The general formula (2) has only to be such that a total of pX's and a total of q Y's exist, and the order in which X's and Y's arearranged is not limited. The order of X and Y may be inverted likeA²-R⁶—Y_(q)—X_(p)—R⁷. In addition, the “X_(p)” part in the generalformula (2) may be such that the p X's are not continuous. Similarly,the “Y_(q)” part may be such that the q Y's are not continuous. X's andY's may be alternately arranged, or X's and Y's may be arranged atrandom like, for example, —XXYXYY—.

In the general formulae (1) and (2), A¹ and A² each represent preferablya hydrolyzable group, more preferably a hydrocarbyloxy group or ahalogen atom. The hydrocarbyloxy group is more preferably an alkoxygroup having 1 to 12 carbon atoms, a phenoxy group, or a benzyloxygroup. R¹ and R⁶ each preferably represent a single bond. R² and R⁸ eachpreferably represent a divalent aliphatic hydrocarbon group having 1 to20 carbon atoms or a divalent aromatic hydrocarbon group having 6 to 18carbon atoms.

In addition, that R¹ in the general formula (1) represents a single bondmeans that A¹ and Si are directly bonded to each other through thesingle bond, that R⁶ in the general formula (2) represents a single bondmeans that A² and Si are directly bonded to each other through thesingle bond, and the same holds true for any other case.

Described here is an example of the modifying agent in the presentinvention obtained by hydrolyzing the silicon-containing compound havinga protected primary amino group and at least two hydrolyzable groups tocondensate the compound via a silanol group, in particular, tocompletely condensate the compound.

The formula (3) represents a raw material for the modifying agent andthe formula (4) represents the modifying agent to be used in the step ofmodifying a diene-based copolymer, the modifying agent being obtained byhydrolyzing the raw material to completely condensate the raw material.

(In the formulae (3) and (4), R^(a) represents a divalent hydrocarbongroup having 1 to 20 carbon atoms, R^(b) and R^(d) each represent ahydrolyzable group (preferably a hydrocarbyloxy group or a halogenatom), R^(b) represents a hydrolyzable group (preferably ahydrocarbyloxy group or a halogen atom) or a hydrocarbyl group, TMSrepresents a trimethylsilyl group as a protective group for a primaryamino group, and m represents 2 to 20.)

The formula (4) is obtained by the condensation of disilanol compoundsand condensation with a monosilanol compound for sealing an end of theresultant, and m represents the condensation degree of the formula,which is preferably 2 to 20, particularly preferably 2 to 10.

In addition, the active site at an end of the polymer (conjugateddiene-based polymer) can react with any one of R^(b) and R^(d) of themodifying agent.

The silicon-containing compound represented by the formula (3) is, forexample, a hydrocarbyloxysilane compound having a protected primaryamino group having, as protective groups, two trialkylsilyl groups eachrepresented by —SiR^(e)R^(f)R^(g) (where R^(e), R^(f), and R^(g) eachindependently represent an alkyl group having 1 to 12 carbon atoms,preferably a methyl group, an ethyl group, a propyl group, or a butylgroup). Specific examples of the hydrocarbyloxysilane compound having aprotected primary amino group preferably includeN,N-bis(trimethylsilyl)aminopropyltrimethoxysilane,N,N-bis(trimethylsilyl)aminopropylmethyltriethoxysilane,N,N-bis(trimethylsilyl)aminopropylmethyldimethoxysilane,N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane,N,N-bis(trimethylsilyl)aminoethylmethyldimethoxysilane, andN,N-bis(trimethylsilyl)aminoethylmethyldiethoxysilane. Of those,N,N-bis(trimethylsilyl)aminopropylmethyldimethoxysilane andN,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane are particularlypreferred.

Examples of the compounds which has a halogen atom includeN,N-bis(trimethylsilyl)aminopropylmethylmethoxychlorosilane,N,N-bis(trimethylsilyl)aminopropylmethylethoxychlorosilane,N,N-bis(trimethylsilyl)aminoethylmethylmethoxychlorosilane, andN,N-bis(trimethylsilyl)aminoethylmethylethoxychlorosilane.

N,N-bis(trimethylsilyl)aminopropyltrimethoxysilane,N,N-bis(trimethylsilyl)aminopropylmethyltriethoxysilane,N,N-bis(trimethylsilyl)aminopropylmethyldimethoxysilane,N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane, and1-trimethylsilyl-2-ethoxymethyl-1-aza-2-cyclopentane are preferred, andcomplete condensation products thereof are utilized as a modifyingagent. Those modifying agents may be used alone or in combination of twoor more kinds thereof. However, partial condensation products areutilized as a modifying agent but with little effect.

In this case, the partial condensation product is a compound prepared byconverting a part (not all) of SiOR in the modifying agent to a SiOSibond by condensation.

The hydrocarbyloxysilane compound having a protected primary amino groupis preferred, and the introduction of the primary amino group into amolecular chain end of a modified conjugated diene-based polymersignificantly improves the low heat generating property of a rubbercomposition into which the modified conjugated diene-based polymer iscompounded.

In addition, the use of a complete condensation product as a modifyingagent can achieve, for example, an improvement in abrasion resistance ascompared with a conventional modifying agent because the use improves,in particular, an affinity between silica and the polymer at a modifyinggroup portion that exerts a reinforcing effect.

When the modifying agent obtained by condensing the silicon-containingcompound having a protected primary amino group and at least twohydrolyzable groups is used in the production of a modified conjugateddiene-based polymer of the present invention, the number of functionalgroups per unit modified conjugated diene-based polymer increases.Accordingly, a rubber composition having an increased affinity for afiller such as silica or carbon black, and excellent in low heatgenerating property and abrasion resistance is obtained. As a silanolgroup produced by the hydrolysis of a hydrolyzable functional group sitehas higher reactivity with silica, a rubber composition more excellentin low heat generating property and abrasion resistance is obtained.

In addition, a method of producing the modified conjugated diene-basedpolymer of the present invention is characterized by comprising: amodifying step of causing the modifying agent to react with an activesite of the conjugated diene-based polymer having the active site tomodify the polymer; and a deprotecting step to be performed after thecompletion of the modifying step. Through the deprotecting step, aprotective group leaves from the protected primary amino group so that aprimary amino group may be produced.

The production method of the present invention preferably furthercomprises a hydrolyzing step between the modifying step and thedeprotecting step, or after the deprotecting step or simultaneously withthe deprotecting step. The method preferably comprises (a) the modifyingstep of causing the modifying agent to react with an active site of theconjugated diene-based polymer having the active site to modify thepolymer and (b) a hydrolyzing step to be performed after the completionof the modifying step. Through such step, a silanol group is providedfor a molecular chain end of the modified conjugated diene-based polymerof the present invention.

In the present invention, the hydrolyzable group that produces a silanolgroup by hydrolysis is an alkoxysilane group or a halogen atom, and ismore preferably such that 10% or more of the compound produces a silanolgroup by hydrolysis in terms of an effect of the present invention. Theprotective group of the protected primary amino group is preferably ahydrolyzable protective group because the deprotecting step and thehydrolyzing step can be simultaneously performed.

It should be noted that the term “conjugated diene-based polymer” in thepresent invention comprehends a conjugated diene polymer and aconjugated diene copolymer.

When the characteristic group that produces a silanol group byhydrolysis reacts with a reinforcing filler, in particular, silica, thegroup needs to turn into a silanol group by the reaction. However, whenthe group is a silanol group from the start, the following large effectsare exerted. Reactivity with silica becomes higher, the dispersibilityof silica in a rubber composition is improved, and the low heatgenerating property of the rubber composition is improved. Further, thecase where the characteristic group that produces a silanol group byhydrolysis is an alkoxy group is preferred in terms of a workingenvironment because a volatile organic compound (VOC, especially analcohol) is generated but no silanol group is generated.

A conjugated diene monomer to be used in the modified conjugateddiene-based polymer in the method of producing the modified conjugateddiene-based polymer of the present invention is preferably, for example,1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene,2-phenyl-1,3-butadiene, or 1,3-hexadiene. They may be used alone or incombination of two or more kinds thereof. Of those, one kind selectedfrom 1,3-butadiene, isoprene, and 2,3-dimethyl-1,3-butadiene is morepreferred, and 1,3-butadiene is particularly preferred.

Further, an aromatic vinyl monomer to be used in the conjugateddiene-based polymer is, for example, styrene, α-methylstyrene,1-vinylnaphthalene, 3-vinyltoluene, ethylvinylbenzene, divinylbenzene,4-cyclohexylstyrene, and 2,4,6-trimethylstyrene. They may be used aloneor in combination of two or more kinds thereof. Of those, styrene isparticularly preferred.

The conjugated diene-based polymer in the method of producing themodified conjugated diene-based polymer of the present invention ispreferably a polybutadiene, a polyisoprene, a butadiene-isoprenecopolymer, a styrene-butadiene copolymer, a styrene-isoprene copolymer,or a styrene-isoprene-butadiene terpolymer. Of those, the polybutadieneand the styrene-butadiene copolymer are particularly preferred.

The method of producing the modified conjugated diene-based polymer ofthe present invention is described in detail. In order that the activesite of the conjugated diene-based polymer and an organosilane compoundin the modifying step of the production method of the present inventionmay be caused to react with each other, the conjugated diene-basedpolymer to be used is preferably such that at least 10% of its polymerchains have living property or pseudo-living property. A polymerizationreaction having such living property is preferably anionicpolymerization or coordination anionic polymerization. Of those, theanionic polymerization is particularly preferred because thepolymerization does not require the preliminary modifying step.

Although the active site of the conjugated diene-based polymer in themodifying step of the production method of the present invention may beany one of the active site (active site at a molecular chain end) of theconjugated diene-based polymer, an active site in its main chain, and anactive site in a side chain thereof, the active site of the conjugateddiene-based polymer is preferably an active end when the active site isobtained by anionic polymerization or coordination anionicpolymerization.

The production method of the present invention is preferably such thatthe conjugated diene-based polymer having an active site is obtained bysubjecting a conjugated diene compound alone, or the conjugated dienecompound and an aromatic vinyl compound, to anionic polymerization withan organic alkali metal compound as a polymerization initiator.

An organic lithium compound is preferably used as the organic alkalimetal compound to be used as the initiator for the anionicpolymerization described above. No particular limitation is imposed onthe organic lithium compound, and a hydrocarbyllithium and a lithiumamide compound are preferably used. When the hydrocarbyllithium is used,a conjugated diene polymer and a conjugated diene-based polymer eachhaving a hydrocarbyl group at a polymerization-initiating end and apolymerization active site at the other end are produced. Further, whenthe lithium amide compound is used, a conjugated diene polymer and aconjugated diene-based polymer each having a nitrogen-containing groupat a polymerization-initiating end and a polymerization active site atthe other end are produced.

The hydrocarbyllithium is preferably a compound having a hydrocarbylgroup having 2 to 20 carbon atoms. Examples thereof includeethyllithium, n-propyllithium, isopropyllithium, n-butyllithium,sec-butyllithium, tert-octyllithium, n-decyllithium, phenyllithium,2-naphthyllithium, 2-butyl-phenyllithium, 4-phenyl-butyllithium,cyclohexyllithium, cyclopentyllithium, and a reaction product ofdiisopropenylbenzene with butyllithium. Of those, n-butyllithium isparticularly suited.

On the other hand, the lithium amide compound includes, for example,lithium hexamethyleneimide, lithium pyrrolidide, lithium piperidide,lithium heptamethyleneimide, lithium dodecamethyleneimide, lithiumdimethylamide, lithium diethylamide, lithium dibutylamide,lithiumdipropylamide, lithiumdiheptylamide, lithium dihexylamide,lithium dioctylamide, lithium di-2-ethylhexylamide, lithiumdidecylamide, lithium-N-methylpiperazide, lithium ethylpropylamide,lithium ethylbutylamide, lithium ethylbenzylamide, and lithiummethylphenethylamide. Of those, cyclic lithium amides such as lithiumhexamethyleneimide, lithium pyrrolidide, lithium piperidide, lithiumheptamethyleneimide, and lithium dodecamethyleneimide are preferred interms of interaction with carbon black and polymerization initiatingability. Particularly suited are lithium hexamethyleneimide and lithiumpyrrolidide.

Generally, those lithium amide compounds for use in polymerization maybe prepared in advance from a secondary amine and a lithium compound.Alternatively, the amide compounds may also be prepared in thepolymerization system (in-situ). The usage of the polymerizationinitiator is preferably selected in the range of 0.2 to 20 mmol per 100g of the monomer.

No particular limitation is imposed on the method of producing aconjugated diene-based polymer through anionic polymerization employingthe organic lithium compound serving as a polymerization initiator, andany conventionally known methods may be employed.

Specifically, in an organic solvent which is inert to the reaction suchas a hydrocarbon-based solvent including aliphatic, alicyclic, andaromatic hydrocarbon compounds, a conjugated diene monomer or a mixtureof a conjugated diene monomer and an aromatic vinyl monomer isanionically polymerized in the presence of the lithium compound servingas a polymerization initiator and an optional randomizer, therebyproducing a conjugated diene-based polymer of interest having an activesite.

In addition, in the case where the organic lithium compound is used asthe polymerization initiator, not only the conjugated diene polymerhaving an active site but also the conjugated diene-aromatic vinylcopolymer having an active site can be obtained with higher efficiencythan that in the case where the catalyst containing a lanthanum seriesrare earth element compound is used.

The hydrocarbon-based solvent is preferably a hydrocarbon having 3 to 8carbon atoms. Examples thereof include propane, n-butane, isobutane,n-pentane, isopentane, n-hexane, cyclohexane, propene, 1-butene,isobutene, trans-2-butene, cis-2-butene, 1-pentene, 2-pentene, 1-hexene,2-hexene, benzene, toluene, xylene, and ethylbenzene. They may be usedalone or in combination of two or more kinds thereof.

In addition, a monomer concentration in the solvent is preferably 5 to50 mass %, more preferably 10 to 30 mass %. It should be noted that,when copolymerization is carried out with the conjugated diene monomerand the aromatic vinyl monomer, the content of the aromatic vinylmonomer in a mixture of the loaded monomers preferably falls within therange of 55 mass % or less.

Further, the randomizer, which may be used in accordance with needs, isa compound which is capable of controlling a microstructure of aconjugated diene-based polymer such as increasing 1,2-bonds of thebutadiene moieties in a styrene-butadiene copolymer or 3,4-bonds in anisoprene polymer or controlling the monomer unit compositiondistribution in a conjugated diene-aromatic vinyl copolymer such asrandomizing butadiene units and styrene units in a styrene-butadienecopolymer. No particular limitation is imposed on the type ofrandomizer, and any of known compounds conventionally used as arandomizer may appropriately employed. Specific examples of therandomizer include ethers and tertiary amines such as dimethoxybenzene,tetrahydrofuran, dimethoxyethane, diethylene glycol dibutyl ether,diethylene glycol dimethyl ether, 2,2-bis(2-tetrahydrofuryl)-propane,triethylamine, pyridine, N-methylmorpholine,N,N,N′,N′-tetramethylethylenediamine, and 1,2-piperidinoethane. Further,potassium salts such as potassium t-amylate and potassium t-butoxide andsodium salts such as sodium t-amylate may also be employed.

Those randomizers may be used alone or in combination of two or morekinds thereof. The usage of the randomizer is preferably selected in therange of 0.01 to 1000 mole equivalents per mole of the lithium compound.

The temperature of the polymerization reaction is preferably selected inthe range of 0 to 150° C., more preferably 20 to 130° C. Thepolymerization reaction may be carried out under generated pressure, butgenerally desirably performed under such pressure that the monomer ismaintained virtually as a liquid phase. That is, a higher pressure maybe employed in accordance with needs, although depending on theindividual substances to be polymerized, polymerization solvent, andpolymerization temperature. Such pressure may be obtained through anappropriate method such as applying pressure to a reactor by use of gasinert to the polymerization reaction.

In the anionic polymerization, all raw materials involved in thepolymerization such as the polymerization initiator, the solvent, andthe monomer are desirably used after reaction inhibitors such as water,oxygen, carbon dioxide, and a protonic compound have been removed fromthe raw materials.

The polymerization reaction may be performed according to any one of abatch mode and a continuous mode.

Thus, the conjugated diene-based polymer having an active site isobtained.

In the modifying step of the method of producing the modified conjugateddiene-based polymer of the present invention, the modifying agent isadded to the conjugated diene-based polymer having an active siteobtained as described above preferably in a stoichiometric amount withrespect to the active site of the conjugated diene-based polymer or anamount in excess thereof so as to be caused to react with the activesite bonded to the polymer.

The modifying step of the present invention is typically performed underthe same temperature and pressure conditions as those of thepolymerization reaction.

The amino group derived from the modifying agent of the modifiedconjugated diene-based polymer of the present invention is preferablydeprotected so as to be converted into a primary amino group. Thefollowing procedure is employed in the deprotecting step of performing adeprotection treatment.

That is, the protected amino group is converted into a free amino groupby the hydrolysis of a silyl protective group on the group. Subjectingthe resultant to a desolvation treatment provides a dry polymer having aprimary amino group. It should be noted that the deprotection treatmentof the protected primary amino group derived from the modifying agentcan be performed as required at any one of the stages ranging from astage involving a condensation treatment to be described later to thestage at which desolvation is performed so that the dry polymer may beobtained. The deprotecting step can be performed simultaneously with thedesolvating step by, for example, steam stripping.

In the present invention, the target modified conjugated diene-basedpolymer can be obtained by performing the following deprotecting step. Agroup derived from a silicon atom compound bonded to the active end ofthe conjugated diene-based polymer is subjected to a hydrolysistreatment so that the protected primary amino group in the group may beconverted into an amino group as a free radical.

In the hydrolyzing step in the production method of the presentinvention to be preferably provided between the modifying step and thedeprotecting step, or after the deprotecting step or simultaneously withthe deprotecting step, a hydrolysis reaction is performed after thecompletion of the modifying step in the presence of water under anacidic, neutral, or alkaline condition. Thus, the hydrolyzablefunctional group bonded to the modified conjugated diene-based polymeris efficiently hydrolyzed so that a silanol group may be produced at anend or side chain of the modified conjugated diene-based polymer.

The amount of water to be used in the hydrolysis reaction is preferablya molar amount in excess of the molar amount of Li of the initiator, forexample, such as a molar amount two to four times as large as the molaramount of Li of the initiator. A hydrolysis time is typically about tenminutes to several hours.

It should be noted that when the hydrolysis reaction is performed underan alkaline condition, an alkali metal hydroxide such as sodiumhydroxide or potassium hydroxide, preferably sodium hydroxide isdesirably added as a basic compound, and when the hydrolysis reaction isperformed under an acidic condition, an inorganic acid such ashydrochloric acid, sulfuric acid, or nitric acid, a carboxylic acid suchas acetic acid or formic acid, silicon tetrachloride, or the like isdesirably added as an acidic compound.

In the foregoing, that the hydrolyzing step is performed simultaneouslywith the deprotecting step means that the deprotecting step and thehydrolyzing step are performed in a single step.

In the present invention, a condensation reaction step of performing acondensation reaction in the presence of a condensation-acceleratingagent can be further provided between the modifying step and thedeprotecting step or the hydrolyzing step.

The condensation-accelerating agent to be used in the condensationreaction is preferably added after the modification reaction and beforethe initiation of the condensation reaction. When thecondensation-accelerating agent is added before the modificationreaction, its direct reaction with an active site occurs and hence ahydrocarbyloxy group is not introduced into the active site in somecases. In addition, when the condensation-accelerating agent is addedafter the initiation of the condensation reaction, thecondensation-accelerating agent is not uniformly dispersed and hence itscatalytic performance reduces in some cases.

When the condensation reaction step is provided between the modifyingstep and the hydrolyzing step, the timing at which thecondensation-accelerating agent is added is typically 5 minutes to 5hours after the initiation of the modification reaction, preferably 15minutes to 1 hour after the initiation of the modification reaction.When the condensation reaction step is provided after the hydrolyzingstep, the timing is typically 5 minutes to 5 hours after the initiationof the hydrolysis reaction, preferably 10 minutes to 2 hours after theinitiation.

The condensation-accelerating agent is preferably a compound containinga metal element, and is more preferably a compound containing at leastone kind of metal belonging to any one of Groups 2 to 15 of the periodictable.

The condensation-accelerating agent containing a metal element issuitably as described below. The agent contains at least one kindselected from Ti, Sn, Bi, Zr and Al, and is an alkoxide, carboxylate, oracetylacetonate complex salt of the metal.

An alkoxide, carboxylate, and acetylacetonate complex salt of titanium(Ti) are each preferably used as a condensation-accelerating agentcontaining Ti as a metal component.

Specific examples thereof includetetrakis(2-ethyl-1,3-hexanediolato)titanium,tetrakis(2-methyl-1,3-hexanediolato)titanium,tetrakis(2-propyl-1,3-hexanediolato)titanium,tetrakis(2-butyl-1,3-hexanediolato)titanium,tetrakis(1,3-hexanediolato)titanium,tetrakis(1,3-pentanediolato)titanium,tetrakis(2-methyl-1,3-pentanediolato)titanium,tetrakis(2-ethyl-1,3-pentanediolato)titanium,tetrakis(2-propyl-1,3-pentanediolato)titanium,tetrakis(2-butyl-1,3-pentanediolato)titanium,tetrakis(1,3-heptanediolato)titanium,tetrakis(2-methyl-1,3-heptanediolato)titanium,tetrakis(2-ethyl-1,3-heptanediolato)titanium,tetrakis(2-propyl-1,3-heptanediolato)titanium,tetrakis(2-butyl-1,3-heptanediolato)titanium,tetrakis(2-ethylhexoxy)titanium, tetramethoxytitanium,tetraethoxytitanium, tetra-n-propoxytitanium, tetraisopropoxytitanium,tetra-n-butoxytitanium, a tetra-n-butoxytitanium oligomer,tetraisobutoxytitanium, tetra-sec-butoxytitanium,tetra-tert-butoxytitanium, bis(oleato)bis(2-ethylhexanoato)titanium,titanium dipropoxybis(triethanolaminate), titaniumdibutoxybis(triethanolaminate), titanium tributoxystearate, titaniumtripropoxystearate, titanium tripropoxyacetylacetonate, titaniumdipropoxybis(acetylacetonate), titanium tripropoxy(ethylacetoacetate),titanium propoxyacetylacetonatobis(ethylacetoacetate), titaniumtributoxyacetylacetonate, titanium dibutoxybis (acetylacetonate),titanium tributoxyethylacetoacetate, titaniumbutoxyacetylacetonatobis(ethylacetoacetate), titaniumtetrakis(acetylacetonate), titaniumdiacetylacetonatobis(ethylacetoacetate), bis(2-ethylhexanoato) titaniumoxide, bis(laurato) titanium oxide, bis(naphthenato)titanium oxide,bis(stearato)titanium oxide, bis(oleato)titanium oxide,bis(linolato)titanium oxide, tetrakis(2-ethylhexanoato)titanium,tetrakis(laurato)titanium, tetrakis(naphthenato)titanium,tetrakis(stearato)titanium, tetrakis(oleato)titanium,tetrakis(linolato)titanium, titaniumdi-n-butoxide(bis-2,4-pentanedionate), titanium oxide bis(stearate),titanium oxide bis(tetramethylheptanedionate), titanium oxidebis(pentanedionate), and titanium tetra(lactate).

Of those, tetrakis(2-ethyl-1,3-hexanediolato)titanium,tetrakis(2-ethylhexoxy)titanium, and titaniumdi-n-butoxide(bis-2,4-pentanedionate) are preferred.

A condensation-accelerating agent containing Sn as a metal complex ispreferably a tin compound having an oxidation number of 2 represented bySn (OCOR³¹)₂ (where R³¹ represents an alkyl group having 2 to 19 carbonatoms) or a tin compound having an oxidation number of 4 represented byR³², SnA⁵ _(y) B¹ _(4-y-x) (where R³² represents an aliphatichydrocarbon group having 1 to 30 carbon atoms, x represents an integerof 1 to 3, y represents 1 or 2, A⁵ represents a group selected from acarboxyl group having 2 to 30 carbon atoms, a β-dicarbonyl group having5 to 20 carbon atoms, a hydrocarbyloxy group having 3 to 20 carbonatoms, and a siloxy group trisubstituted with a hydrocarbyl group having1 to 20 carbon atoms and/or a hydrocarbyloxy group having 1 to 20 carbonatoms, and B¹ represents a hydroxyl group or a halogen atom).

More specifically, a dicarboxylate of divalent tin, a dicarboxylate(comprehending a bis(hydrocarbyldicarboxylate)), bis(β-diketonate),alkoxy halide, monocarboxylic acid salt hydroxide,alkoxy(trihydrocarbylsiloxide), alkoxy(dihydrocarbylalkoxysiloxide),bis(trihydrocarbylsiloxide), or bis(dihydrocarbylalkoxysiloxide) oftetravalent dihydrocarbyltin, or the like can be suitably used as thecarboxylate of tin. A hydrocarbyl group bonded to tin is desirably agroup having 4 or more carbon atoms, and is particularly preferably agroup having 4 to 8 carbon atoms.

In addition, a condensation-accelerating agent containing Zr, Bi, or Alas a metal component (such as an alkoxide, carboxylate, oracetylacetonate complex salt of any such metal) is, for example, any oneof the following compounds (a) to (e).

(a) carboxylic acid salt of bismuth

(b) alkoxide of zirconium

(c) carboxylic acid salt of zirconium

(d) alkoxide of aluminum

(e) carboxylic acid salt of aluminum

Specific examples thereof include: tris(2-ethylhexanoato)bismuth,tris(laurato)bismuth, tris(naphthenato)bismuth, tris(stearato)bismuth,tris(oleato)bismuth, and tris(linolato)bismuth; tetraethoxyzirconium,tetra-n-propoxyzirconium, tetra-isopropoxyzirconium,tetra-n-butoxyzirconium, tetra-sec-butoxyzirconium,tetra-tert-butoxyzirconium, tetra(2-ethylhexoxy)zirconium, zirconiumtributoxystearate, zirconium tributoxyacetylacetonate, zirconiumbutoxybis(acetylacetonate), zirconium tributoxyethylacetoacetate,zirconium butoxyacetylacetonatobis(ethylacetoacetate), zirconiumtetrakis(acetylacetonate), zirconiumdiacetylacetonatobis(ethylacetoacetate),bis(2-ethylhexanoato)zirconiumoxide, bis(laurato)zirconiumoxide,bis(naphthenato)zirconium oxide, bis(stearato)zirconium oxide,bis(oleato)zirconium oxide, bis(linolato)zirconium oxide,tetrakis(2-ethylhexanoato)zirconium, tetrakis(laurato)zirconium,tetrakis(naphthenato)zirconium, tetrakis(stearato)zirconium,tetrakis(oleato)zirconium, and tetrakis(linolato)zirconium; andtriethoxyaluminum, tri-n-propoxyaluminum, triisopropoxyaluminum,tri-n-butoxyaluminum, tri-sec-butoxyaluminum, tri-tert-butoxyaluminum,tri(2-ethylhexoxy)aluminum, aluminum dibutoxystearate, aluminumdibutoxyacetylacetonate, aluminum butoxybis(acetylacetonate), aluminumdibutoxyethylacetoacetate, aluminum tris(acetylacetonate), aluminumtris(ethylacetoacetate), tris(2-ethylhexanoato)aluminum,tris(laurato)aluminum, tris(naphthenato)aluminum,tris(stearato)aluminum, tris(oleato)aluminum, andtris(linolato)aluminum.

Of those, tris(2-ethylhexanoato)bismuth, tetra-n-propoxyzirconium,tetra-n-butoxyzirconium, bis(2-ethylhexanoato) zirconium oxide,bis(oleato) zirconium oxide, triisopropoxyaluminum,tri-sec-butoxyaluminum, tris(2-ethylhexanoato)aluminum,tris(stearato)aluminum, zirconium tetrakis(acetylacetonate), andaluminum tris(acetylacetonate) are preferred.

The compounding amount (usage) of the condensation-accelerating agent ispreferably such an amount as to be 0.1 to 10 parts by mass based on 100parts by mass of the rubber component in a rubber composition to bedescribed later. The compounding amount is more preferably 0.5 to 5parts by mass. Setting the usage of the condensation-accelerating agentwithin the range allows the condensation reaction to progressefficiently.

The condensation reaction is preferably carried out in an aqueoussolution, and the temperature during the condensation reaction ispreferably 85 to 180° C., more preferably 100 to 170° C., particularlypreferably 110 to 150° C. Through controlling the temperature during thecondensation reaction to fall within the range, the condensationreaction can be efficiently completed, whereby deterioration in qualityand the like of the produced modified conjugated diene-based polymerbecause of time-dependent aging reaction of the polymer and the like canbe prevented.

It should be noted that the condensation reaction time is preferablyabout 5 minutes to 10 hours, more preferably about 15 minutes to 5hours. Through controlling the condensation reaction time to fall withinthe range, the condensation reaction can be smoothly completed.

The pressure of the reaction system during the condensation reaction ispreferably 0.01 to 20 MPa, more preferably 0.05 to 10 MPa.

No particular limitation is imposed on the mode with which thecondensation reaction is performed, and a batch-type reactor may beemployed. Alternatively, the reaction may be carried out in a continuousmanner by means of an apparatus such as a multi-step continuous reactor.In the course of the condensation reaction, desolvation may besimultaneously performed.

After the completion of the deprotecting step or of the deprotectingstep and the condensation reaction step, for example, a solution of2,6-di-t-butyl-p-cresol (BHT) in isopropanol is added to apolymerization reaction system to terminate the polymerization reaction.

After that, a desolvation treatment such as steam stripping involvingblowing in steam to reduce the partial pressure of the solvent or avacuum drying treatment is performed. Thus, the modified conjugateddiene-based polymer of the present invention is obtained.

Here, when the hydrocarbyloxysilane compound having a protected primaryamino group is used in the modifying step, a deprotection treatment inwhich the protective group of a protected nitrogen atom is caused toleave so that a primary amino group may be produced is simultaneouslyperformed in a desolvation treatment step involving using steam such assteam stripping described above. In addition to the foregoing, thedeprotection treatment of the protected primary amino group derived fromthe hydrocarbyloxysilane compound can be performed by hydrolyzing theprotective group on the primary amino group according to any one of thevarious methods to convert the group into a free primary amino group asrequired at any one of the stages ranging from a stage after thecompletion of the modifying step to the stage at which desolvation isperformed so that a dry polymer may be obtained.

Next, the modified conjugated diene-based polymer obtained by theproduction method of the present invention is described.

The modified conjugated diene-based polymer of the present inventionpreferably has, at a molecular end of the conjugated diene-basedpolymer, a silanol group and a functional group in the vicinity of thesilanol group, the functional group accelerating a reaction between thesilanol group and a reinforcing filler.

The modified conjugated diene-based polymer of the present invention ispreferably such that only one silanol group exists in its molecularchain. This is because of the following reason. When two or more silanolgroups exist in the molecular chain, the silanol groups condense eachother. As a result, the viscosity of the modified conjugated diene-basedpolymer increases, thereby making it difficult to perform its kneadingoperation in some cases.

In addition, the modified conjugated diene-based polymer of the presentinvention has both the silanol group, and the functional group in thevicinity of the silanol group for accelerating the reaction between thesilanol group and the reinforcing filler. Accordingly, low heatgenerating property is improved in each of a silica-compounded rubbercomposition and a carbon black-compounded rubber composition as comparedwith: a modified conjugated diene-based polymer having only a silanolgroup, and free of any functional group for accelerating a reactionbetween the silanol group and the reinforcing filler; and a modifiedconjugated diene-based polymer having only a functional group foraccelerating a reaction between a silanol group and the reinforcingfiller, and free of any silanol group.

In the present invention, a primary amino group or a protected primaryamino group is effective as a group for accelerating a reaction with thefiller.

The vinyl bond content of the conjugated diene portion of the modifiedconjugated diene-based polymer of the present invention, which is notlimited, is preferably 70% or less. A vinyl bond content of 70% or lessis preferred because a fracture characteristic and an abrasioncharacteristic are improved when the polymer is used in a tire tread.

In addition, the polymer preferably has a styrene content of 0 to 50mass %. This is because a styrene content of 50 mass % or less improvesa balance between its low heat generating property and wet skidperformance.

It should be noted that the vinyl bond content was determined by aninfrared method (Morero method) and the styrene content was determinedby calculating the integration ratio of a ¹H-NMR spectrum.

A rubber composition of the present invention contains the modifiedconjugated diene-based polymer of the present invention, and preferablyfurther contains a condensation-accelerating agent.

The modified conjugated diene-based polymer to be incorporated as anessential component into the rubber composition of the present inventionmay be a modified conjugated diene-based polymer obtained by theproduction method of the present invention, the polymer being obtainedby performing a modification reaction, a deprotection reaction, and insome cases, a condensation reaction involving using acondensation-accelerating agent, or may be a modified conjugateddiene-based polymer obtained without through the condensation reactioninvolving using a condensation-accelerating agent.

The rubber composition of the present invention can further contain acondensation-accelerating agent.

The condensation-accelerating agent may be added at the time of thesynthesis of the modified conjugated diene-based polymer like theproduction method of the present invention, or may be added at the timeof the preparation of the rubber composition. Alternatively, thoseoperations may be combined.

Information about the condensation-accelerating agent is as described inthe condensation reaction in the method of producing a modifiedconjugated diene-based polymer.

When the condensation-accelerating agent is added at the time of thepreparation of the rubber composition, the agent is preferably kneadedwith any other component at a first stage at a temperature of typicallyabout 20 to 185° C., more preferably 60 to 175° C.

The content of the condensation-accelerating agent in the rubbercomposition is preferably 0.1 to 10 parts by mass based on 100 parts bymass of the rubber component from the viewpoint of reactivity betweensilica and silanol, and is more preferably 0.5 to 5 parts by mass.

The rubber component of the rubber composition of the present inventionis preferably formed of 10 to 100 mass % of the modified conjugateddiene-based polymer and 90 to 0 mass % of diene-based rubber. This isbecause when the content of the modified conjugated diene-based polymeris 10 mass % or more, the effect of the present invention can beenjoyed. Here, examples of the diene-based rubber include apolybutadiene, a polyisoprene, a polybutadiene-polyisoprene copolymer, astyrene-butadiene copolymer, a styrene-isoprene copolymer, astyrene-isoprene-butadiene terpolymer, an ethylene-propylene-dieneterpolymer, a butyl rubber, and a halogenated butyl rubber except themodified conjugated diene-based polymer according to the presentinvention.

The rubber composition of the present invention contains preferably 10to 200 parts by mass, more preferably 20 to 120 parts by mass,particularly preferably 30 to 100 parts by mass of a reinforcing fillerbased on 100 parts by mass of the rubber component formed of 10 to 100mass % of the modified conjugated diene-based polymer of the presentinvention and 90 to 0 mass % of a diene-based rubber. In addition, thereinforcing filler is preferably carbon black and/or silica. Thereinforcing filler is particularly preferably silica.

Carbon black to be used as the reinforcing filler is not particularlylimited, and for example, a GPF, FEF, SRF, HAF, N339, IISAF, ISAF, orSAF is used. Carbon black having a nitrogen adsorption specific surfacearea (N₂SA, measured in conformity with JIS K 6217-2:2001) of 20 to 250m²/g is preferred.

Any one of the various commercial products can be used as silica to beused as the reinforcing filler in combination with carbon black asdesired or alone. Of those, wet silica, dry silica, or colloidal silicais preferably used, and wet silica is particularly preferably used. TheBET specific surface area (measured in conformity with ISO 5794/1) ofsilica is preferably 100 m²/g or more, more preferably 150 m²/g or more,particularly preferably 170 m²/g or more. A commercial product such as aproduct available under the trade name “Nipsil AQ” (BET specific surfacearea-190 m²/g) or “Nipsil KQ” from TOSOH SILICA CORPORATION, or aproduct available under the trade name “Ultrasil VN3” (BET specificsurface area=175 m²/g) from Degussa can be used as such silica.

When silica is used as a filler in the rubber composition of the presentinvention, a silane coupling agent can be compounded thereinto for thepurpose of further improving the reinforcing property and the low heatgenerating property.

The silane coupling agent includes, for example,bis(3-triethoxysilylpropyl)tetrasulfide,bis(3-triethoxysilylpropyl)trisulfide,bis(3-triethoxysilylpropyl)disulfide,bis(2-triethoxysilylethyl)tetrasulfide,bis(3-trimethoxysilylpropyl)tetrasulfide,bis(2-trimethoxysilylethyl)tetrasulfide,3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane,2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane,3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide,3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide,2-triethoxysilylethyl-N,N-dimethylthiocarbamonyl tetrasulfide,3-trimethoxysilylpropylbenzothiazolyl tetrasulfide,3-triethoxysilylpropylbenzolyl tetrasulfide,3-triethoxysilylpropylmethacrylate monosulfide,3-trimethoxysilylpropylmethacrylate monosulfide,bis(3-diethoxymethylsilylpropyl)tetrasulfide,3-mercaptopropyldimethoxymethylsilane,dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, anddimethoxymethylsilylpropylbenzothiazolyl tetrasulfide. Of those,bis(3-triethoxysilylpropyl)polysulfide and3-trimethoxysilylpropylbenzothiazyl tetrasulfide are suited in terms ofan effect of improving the reinforcing property and the like.

Those silane coupling agents may be used alone or in combination of twoor more kinds thereof.

The rubber composition of the present invention employs, as a rubbercomponent, a modified polymer in which a functional group having a highaffinity to silica is introduced into an active site of the moleculethereof. Therefore, the compounding amount of the silane coupling agentcan be reduced as compared to the general cases. The compounding amountof the silane coupling agent, which varies depending on the kind of theagent, preferably falls within the range of 1 to 20 mass % based onsilica. When the amount falls within the range, gelation of the rubbercomponent may be prevented while attaining the effect of the couplingagent sufficiently. From the viewpoints of the effect of coupling agentand prevention of gelation, the compounding amount of the silanecoupling agent preferably falls within the range of 5 to 15 mass %.

The rubber composition according to the present invention is preferablysulfur-crosslinkable and sulfur is suitably used as a vulcanizing agent.With regard to its usage, a sulfur content (total amount of sulfur andthe sulfur content of a sulfur-donating agent) is preferably compoundedin an amount of 0.1 to 10 parts by mass based on 100 parts by mass ofthe rubber component. This is because when the usage falls within therange, an elastic modulus and strength required of a vulcanized rubbercomposition are secured, and low fuel consumption can be obtained. Fromthe viewpoint, the sulfur content is more preferably compounded in anamount of 0.2 to 8 parts by mass.

Any one of the various chemicals to be typically used in the rubberindustry such as a vulcanizing agent except sulfur, avulcanization-accelerating agent, a process oil, a plasticizer, anantioxidant, a scorch preventive, zinc white, stearic acid, athermosetting resin, and a thermoplastic resin can be incorporated intothe rubber composition according to the present invention as desired tosuch an extent that the object of the present invention is not impaired.

The vulcanization-accelerating agent which can be used in the presentinvention is not specifically limited, and may include thiazole-basedvulcanization-accelerating agents such as 2-mercaptobenzothiazole (M),dibenzothiazyl disulfide (DM), andN-cyclohexyl-2-benzothiazylsulfenamide (CZ), and guanidine-basedvulcanization-accelerating agents such as diphenylguanidine (DPG). Theusage thereof is preferably 0.1 to 5.0 parts by mass, more preferably0.2 to 3.0 parts by mass based on 100 parts by mass of the rubbercomponent.

In addition, the process oil which can be used as a softening agent inthe rubber composition of the present invention includes aparaffin-based oil, a naphthene-based oil, and an aromatic-based oil.The aromatic-based oil is used for uses in which the tensile strengthand the abrasion resistance are regarded as important, and thenaphthene-based oil or the paraffin-based oil is used for uses in whichthe hysteresis loss and the low-temperature characteristic are regardedas important. The usage thereof is preferably 0 to 100 parts by massbased on 100 parts by mass of the rubber component, and when the amountis 100 parts by mass or less, deterioration in the tensile strength andthe low heat generating property (low fuel consumption) of thevulcanized rubber is suppressed.

Further, an antioxidant that can be used in the rubber composition ofthe present invention is, for example,3C(N-isopropyl-N′-phenyl-p-phenylenediamine),6C[N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine],AW(6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline), or a high-temperaturecondensation product of diphenylamine and acetone. The usage of theantioxidant is preferably 0.1 to 6.0 parts by mass, more preferably 0.3to 5.0 parts by mass based on 100 parts by mass of the rubber component.

The rubber composition of the present invention is obtained by kneadingaccording to the compounding formulation with a kneading machine such asa Banbury mixer, a roll, or an internal mixer. The composition issubjected to molding, and is then vulcanized. As a result, a rubbercomposition excellent in low heat generating property and abrasionresistance can be obtained. The rubber composition is used in variousmembers of pneumatic tires and various industrial rubber products suchas a belt conveyor and a rubber hose.

EXAMPLES

Hereinafter, the present invention is described in further details withreference to examples. However, the present invention is by no meanslimited to these examples.

It should be noted that the dynamic loss tangent (tan δ) and abrasionresistance of the vulcanized rubber composition of a modified conjugateddiene-based polymer were measured in accordance with the followingmethods. In addition, the condensation degree (m) of a modifying agentwas measured by the following method.

<Condensation Degree of Modifying Agent> (1) Condensation Degree (m) ofModifying Agent

The condensation degree was calculated froth integration values for boththe peak value of an end portion and a peak value derived from aprotective group in each of GPC and NMR.

<Silanol Production Ratio of Modified Conjugated Diene-Based Polymer>(1) Silanol Production Ratio

The hydrolysis amount of an alkoxysilane group is described in theexample of an ethoxysilyl group. An alkoxysilane amount M (%) of themodified polymer was calculated from a multiband around 3.6 to 3.7 ppmcharacteristic of SiOCH₂CH₃ of the polymer in ¹H-NMR and thenumber-average molecular weight of a base portion. A ratio R_(GPC)% ofan uncoupled component in GPC was calculated from the peak area of abase-equivalent component based on the amount of an injected sample inGPC. In order that a post-reaction component of coupling or the likemight be subtracted, a difference between the M (%) and the R_(GPC)% wasdetermined, and then a silanol production number was calculated from thedifference in terms of percentage. A number-average molecular weightdetermined from GPC corrected with Mark-Houwink's equation was appliedto the number-average molecular weight to be used in the calculation ofthe silanol production ratio.

<Physical Properties of Vulcanized Rubber> (1) Dynamic Loss Tangent (Tanδ)

A tan δ was measured with a viscoelasticity-measuring apparatus(manufactured by Rheometrics, Inc.) at a temperature of 60° C., a strainof 5%, and a frequency of 15 Hz. Shown in Table 1 Was an indexdetermined from the following equation with the tan δ of ComparativeExample 1 set to 100. A smaller index value means that low heatgenerating property is better and hysteresis loss is smaller. Dynamicloss tangent (tan δ) index={(tan δ of vulcanized rubber compositionunder test)/(tan δ of vulcanized rubber composition of ComparativeExample 1, 2, or 5)}×100

(2) Abrasion Resistance (Lambourn)

The result of a JIS K 6264-1993 Lambourn abrasion test was representedas an index calculated from the following equation with the result ofComparative Example 1 or 3 set to 100. Abrasion resistanceindex=(abrasion loss of Comparative Example 1, 2, or 5/abrasion loss ofsample under test)_(x100)

A larger abrasion resistance index means that abrasion resistance ismore excellent.

<Synthesis of Modifying Agent> Synthesis Example 1 Synthesis ofN,N-bis(trimethylsilyl)aminopropyltriethoxysilane

Under a nitrogen atmosphere, 41 g of 3-aminopropyltriethoxysilane(manufactured by Gelest, Inc.) for forming an aminosilane moiety wereadded to 400 ml of a dichloromethane solvent in a glass flask equippedwith a stirring machine. Subsequently, 48 ml of trimethylsilane chloride(manufactured by Sigma-Aldrich, Inc) and 53 ml of triethylamine forforming a protective moiety were added to the solution, followed bystirring the mixture at room temperature for 17 hours. The reactionsolution was then subjected to an evaporator so that the solvent wasremoved. Thus, a composition reaction solution was obtained. Further,the resultant reaction solution was distilled under reduced pressureunder the condition of 5 mm/Hg. Thus, 40 g ofN,N-bis(trimethylsilyl)aminopropyltriethoxysilane were obtained as afraction at 125 to 130° C.

Synthesis Example 2 Synthesis of complete condensation product ofN,N-bis(trimethylsilyl)aminopropyltriethoxysilane

Under a nitrogen atmosphere, 41 g of 3-aminopropyltriethoxysilane(manufactured by Gelest, Inc.) for forming an aminosilane moiety wereadded to 400 ml of a dichloromethane solvent in a glass flask equippedwith a stirring machine. Subsequently, 48 ml of trimethylsilane chloride(manufactured by Sigma-Aldrich, Inc) and 53 ml of triethylamine forforming a protective moiety were added to the solution, followed bystirring the mixture at room temperature for 25 hours. The reactionsolution was then subjected to an evaporator so that the solvent wasremoved. Thus, a composition reaction solution was obtained. Further,the resultant reaction solution was distilled under reduced pressureunder the condition of 5 mm/Hg. Thus, a complete condensation product ofN,N-bis(trimethylsilyl)aminopropyltriethoxysilane was obtained as afraction at 150 to 200° C. The condensation degree m was 4.1.

Synthesis Example 3 Synthesis of complete condensation product ofN,N-bis(trimethylsilyl)aminopropyltriethoxysilane

Under a nitrogen atmosphere, 41 g of 3-aminopropyltriethoxysilane(manufactured by Gelest, Inc.) for forming an aminosilane moiety wereadded to 400 ml of a dichloromethane solvent in a glass flask equippedwith a stirring machine. Subsequently, 48 ml of trimethylsilane chloride(manufactured by Sigma-Aldrich, Inc) and 53 ml of triethylamine forforming a protective moiety were added to the solution, followed bystirring the mixture at 50° C. for 48 hours. The reaction solution wasthen subjected to an evaporator so that the solvent was removed. Thus, acomposition reaction solution was obtained. Further, the resultantreaction solution was distilled under reduced pressure under thecondition of 5 mm/Hg. Thus, a complete condensation product ofN,N-bis(trimethylsilyl)aminopropyltriethoxysilane was obtained as afraction at 150 to 200° C. The condensation degree m was 4.1.

Synthesis Example 4 Synthesis of complete condensation product ofN,N-bis(trimethylsilyl)aminopropyltriethoxysilane andN,N-bis(dimethyl)aminopropyltriethoxysilane

Under a nitrogen atmosphere, 20 g ofN,N-bis(trimethylsilyl)aminopropyltriethoxysilane obtained in SynthesisExample 1 were added to 400 ml of a dichloromethane solvent in a glassflask provided with a stirring machine. After that, a dichloromethanesolution in which 20 g of N,N-bis(dimethyl)aminopropyltriethoxysilanehad been dissolved was dropped while the contents in the flask werestirred under room temperature. After that, the mixture was stirred for25 hours under room temperature, and then the reaction solution wassubjected to an evaporator so that the solvent was removed. Thus, acomposition reaction solution was obtained. Further, the resultantreaction solution was distilled under reduced pressure under thecondition of 5 mm/Hg. Thus, a complete condensation product ofN,N-bis(trimethylsilyl)aminopropyltriethoxysilane andN,N-bis(dimethyl)aminopropyltriethoxysilane was obtained as a fractionat 150 to 200° C.

Synthesis Example 5 Synthesis of ketimine silane condensation product

Under a nitrogen atmosphere, 20.0 g (0.112 mol) of3-aminopropyltrimethoxysilane and 10.7 g (0.123 mol) of methyl isopropylketone were stirred at room temperature for 2 days. Methanol andunreacted methyl isopropyl ketone were removed from the resultantreaction solution under vacuum. Thus, a ketimine silane condensationproduct having an average condensation degree of 2.4 was obtained.

Production Example 1 Production of Modified Conjugated diene copolymer A<Production of Conjugated Diene Copolymer Having Active Site>

A solution of 1,3-butadiene in cyclohexane and a solution of styrene incyclohexane were added to an 800-mL pressure-resistant glass vessel thathad been dried and replaced with nitrogen so that the amount of1,3-butadiene was 60 g and the amount of styrene was 15 g. 0.70Millimole of 2,2-ditetrahydrofurylpropane was added to the mixture.Further, 0.70 mmol of n-butyllithium (BuLi) was added to the mixture,and then the mixture was subjected to a polymerization reaction in a hotwater bath at 50° C. for 1.5 hours. A polymerization conversion degreeat that time was nearly 100%.

<Modifying Step>

Next, the complete condensation product of the organosilane compoundobtained in Synthesis Example 2 was added to the polymerization reactionsystem in an equimolar amount based on lithium (Li). Further, amodification reaction was performed at 50° C. for 30 minutes.

<Hydrolyzing Step and any Subsequent Step>

After that, 1.5 ml of dilute hydrochloric acid were gradually added tothe polymerization reaction system. Next, water was added to thepolymerization reaction system in a molar amount three times as large asthat of lithium (Li), and then the polymerization reaction system wasstirred for 30 minutes. Next, a solution of 2,6-di-tert-butyl-p-cresolin isopropanol was added to the polymerization reaction system toterminate the polymerization reaction. After that, desolvation wasperformed by blowing steam into the system to reduce the partialpressure of the solvent (steam stripping). After that, vacuum drying wasperformed. Thus, a modified conjugated diene copolymer A was obtained.

Production Example 2 Production of Modified Conjugated Diene Copolymer B<Production of Conjugated Diene Copolymer Having Active Site>

A solution of 1,3-butadiene in cyclohexane and a solution of styrene incyclohexane were added to an 800-mL pressure-resistant glass vessel thathad been dried and replaced with nitrogen so that the amount of1,3-butadiene was 60 g and the amount of styrene was 15 g. 0.70Millimole of 2,2-ditetrahydrofurylpropane was added to the mixture.Further, 0.70 mmol of n-butyllithium (BuLi) was added to the mixture,and then the mixture was subjected to a polymerization reaction in a hotwater bath at 50° C. for 1.5 hours. A polymerization conversion degreeat that time was nearly 100%.

<Modifying Step>

Next, the complete condensation product of the organosilane compoundobtained in Synthesis Example 3 was added to the polymerization reactionsystem in an equimolar amount based on lithium (Li). Further, amodification reaction was performed at 50° C. for 30 minutes.

<Any Subsequent Step>

After that, a solution of 2,6-di-tert-butyl-p-cresol in isopropanol wasadded to the polymerization reaction system to terminate thepolymerization reaction. After that, deprotection and desolvation wereperformed by blowing steam into the system to reduce the partialpressure of the solvent (steam stripping). After that, vacuum drying wasperformed. Thus, a modified conjugated diene copolymer B was obtained.

Production Example 3 Production of Modified Conjugated Diene Copolymer C

A modified conjugated diene copolymer C was obtained in the same manneras in Production Example 1 except that no hydrolyzing step was provided.

Production Example 4 Production of Modified Conjugated Diene Copolymer D

A modified conjugated diene copolymer D was obtained in the same manneras in Production Example 1 except that: the complete condensationproduct of N,N-bis(trimethylsilyl)aminopropyltriethoxysilane andN,N-bis(dimethyl)aminopropyltriethoxysilane obtained in SynthesisExample 4 was added as a modifying agent in the modifying step insteadof the complete condensation product ofN,N-bis(trimethylsilyl)aminopropyltriethoxysilane obtained in SynthesisExample 2; and no hydrolyzing step was provided.

Production Comparative Example 1 Production of Modified Conjugated DieneCopolymer E

A modified conjugated diene copolymer E was obtained in the same manneras in Production Example 1 except that the uncondensedN,N-bis(trimethylsilyl)aminopropyltriethoxysilane obtained in SynthesisExample 1 was added as a modifying agent in the modifying step insteadof the complete condensation product ofN,N-bis(trimethylsilyl)aminopropyltriethoxysilane obtained in SynthesisExample 2.

Production Comparative Example 2 Production of Modified Conjugated DieneCopolymer F

A modified conjugated diene copolymer F was obtained in the same manneras in Production Example 2 except that the uncondensedN,N-bis(trimethylsilyl)aminopropyltriethoxysilane obtained in SynthesisExample 1 was added as a modifying agent in the modifying step insteadof the complete condensation product ofN,N-bis(trimethylsilyl)aminopropyltriethoxysilane obtained in SynthesisExample 3.

Production Comparative Example 3 Production of Modified Conjugated DieneCopolymer G

A modified conjugated diene copolymer G was obtained in the same manneras in Production Example 1 except that: the uncondensedN,N-bis(trimethylsilyl)aminopropyltriethoxysilane obtained in SynthesisExample 1 was added as a modifying agent in the modifying step insteadof the complete condensation product ofN,N-bis(trimethylsilyl)aminopropyltriethoxysilane obtained in SynthesisExample 2; and no hydrolyzing step was provided.

Production Comparative Example 4 Production of Modified Conjugated DieneCopolymer H

A modified conjugated diene copolymer H was obtained in the same manneras in Production Example 1 except that: the ketimine silane condensationproduct obtained in Synthesis Example was added as a modifying agent inthe modifying step instead of the complete condensation product ofN,N-bis(trimethylsilyl)aminopropyltriethoxysilane obtained in SynthesisExample 2; and no hydrolyzing step was provided.

Example 1 and Comparative Example 1

The silanol production ratios of the modified conjugated dienecopolymers A and E obtained in Production Example 1 and ProductionComparative Example 1 were measured. In addition, two kinds of rubbercompositions of Example 1 and Comparative Example 1 were each preparedin accordance with the formulation of “Composition 1” shown in Table 1.Table 2 shows the results of the abrasion resistance and tan δ of eachof the rubber compositions after their vulcanization.

Examples 2 to 4 and Comparative Examples 2 to 4

The silanol production ratios of the modified conjugated dienecopolymers A, C, D, E, G, and H obtained in Production Examples 1, 3,and 4 and Production Comparative Examples 1, 3, and 4 were measured. Inaddition, six kinds of rubber compositions of Examples 2 to 4 andComparative Examples 2 to 4 were each prepared in accordance with theformulation of “Composition 2” shown in Table 1. Table 3 shows theresults of the abrasion resistance and tan δ of each of the rubbercompositions after their vulcanization.

Example 5 and Comparative Example 5

The condensation degrees of the modified conjugated diene copolymers Band E obtained in Production Example 2 and Production ComparativeExample 2 were measured. In addition, two kinds of rubber compositionsof Example 2 and Comparative Example 3 were each prepared in accordancewith the compounding formulation shown in Table 1. Table 4 shows theresults of the abrasion resistance and tan δ of each of the rubbercompositions after their vulcanization.

TABLE 1 Kneading Compounding formulation Composition Composition stage(part(s) by mass) 1 2 First Modified conjugated 50 80 Stage diene-basedpolymer *¹ Polyisoprene rubber *² 50 20 Aroma oil *³ 10 10 Carbon black(ISAF-HS) *⁴ 25 30 Silica *⁵ 27.5 25 Silane coupling agent *⁶ 2.75 2.5Stearic acid 2 2 Antioxidant 6C *⁷ 1 1 Second Zinc white 3 3 StageVulcanization-accelerating 0.75 0.75 agent DPG *⁸Vulcanization-accelerating 0.75 0.75 agent DM *⁹Vulcanization-accelerating 0.75 0.75 agent NS *¹⁰ Sulfur 1.5 1.5 [Notes]¹ Modified conjugated diene-based polymer: the modified conjugated dienecopolymers A to H obtained in Production Examples 1 to 4 and ProductionComparative Examples 1 to 4 ² Polyisoprene rubber: a product availableunder the trade name “IR2200” from JSR Corporation ³ Aromatic oil: aproduct available under the trademark “AROMAX #3” from Fuji Kosan Co.,Ltd. ⁴ Carbon black: ISAF-HS ⁵ Silica: a product available under thetrademark “Nipsil AQ” from TOSOH SILICA CORPORATION ⁶ Silane couplingagent: bis(3-triethoxysilylpropyl)tetrasulfide available under thetrademark “Si69” from Degussa ⁷ Antioxidant 6C:N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine available under thetrademark “OZONONE 6C” from Seiko Chemical Co., Ltd. ⁸Vulcanization-accelerating agent DPG: diphenylguanidine available underthe trademark “Nocceler D” from Ouchi Shinko Chemical Industrial Co.,Ltd. ⁹ Vulcanization-accelerating agent DM: dibenzothiazyl disulfideavailable under the trademark “Nocceler DM” from Ouchi Shinko ChemicalIndustrial Co., Ltd. ¹⁰ Vulcanization-accelerating agent NS:N-t-butyl-2-benzothiazylsulfenamide available under the trademark“Nocceler NS” from Ouchi Shinko Chemical Industrial Co., Ltd.

TABLE 2 Comparative Composition 1 Example 1 Example 1 Presence orabsence of condensation Uncondensed Condensed Conjugated diene-basedpolymer *¹ E A Hydrolysis Present Present Silanol production ratio/% 5070 Physical properties of vulcanized rubber (compounded with halfsilica) tanδ (50° C.) (index) 100 88 Abrasion resistance (index) 100 109

TABLE 3 Comparative Comparative Comparative Composition 2 Example 2Example 3 Example 4 Example 2 Example 3 Example 4 Presence or absence ofUncondensed Uncondensed Condensed Condensed Condensed Condensedcondensation Conjugated diene-based G E H A C D polymer*¹ HydrolysisAbsent Present Absent Present Absent Absent Silanol production 2 50 4 706 7 ratio/% Physical properties of vulcanized rubber (compounded withhalf silica) tanδ (50° C.) (index) 100 98 99 88 95 96 Abrasionresistance 100 103 101 111 105 105 (index)

TABLE 4 Comparative Composition 1 Example 5 Example 5 Presence orabsence of condensation Uncondensed Condensed Conjugated diene-basedpolymer *¹ F B Hydrolysis Absent Absent Silanol production ratio/% 5 18Physical properties of vulcanized rubber (compounded with half silica)tanδ (50° C.) (index) 100 97 Abrasion resistance (index) 100 104

INDUSTRIAL APPLICABILITY

The modified conjugated diene-based polymer having low heat generatingproperty and excellent in abrasion resistance obtained by using themodifying agent of the present invention suitably finds use in variousmembers including: treads such as cap treads; sidewalls; and stiffeners(bead fillers); of pneumatic tires for a low heat-generating passengercar, a light car, a light truck, a truck or bus, and an off-the-roadvehicle. In addition, the polymer suitably finds use in various membersof various industrial rubber products such as a belt conveyor and ahose.

1. A modifying agent obtained by subjecting a silicon-containingcompound having a protected primary amino group and at least twohydrolyzable groups to complete condensation.
 2. The modifying agentaccording to claim 1, wherein the hydrolyzable functional groups eachare a group selected from the group consisting of an alkoxy group having1 to 12 carbon atoms, a phenoxy group and a benzyloxy group, or ahalogen atom.
 3. The modifying agent according to claim 1, wherein themodifying agent comprises a compound represented by a general formula(1)

where R¹ and R² each represent a divalent aliphatic hydrocarbon grouphaving 1 to 20 carbon atoms, a divalent aromatic hydrocarbon grouphaving 6 to 18 carbon atoms, or a single bond, and may be identical toor different from each other, R³, R⁴, and R⁵ each represent a monovalentaliphatic hydrocarbon group having 1 to 20 carbon atoms or a monovalentaromatic hydrocarbon group having 6 to 18 carbon atoms, and may beidentical to or different from one another, A¹ represents a group forbonding the modifying agent and a conjugated diene-based polymer byadding to, or substituting for, an active site of the conjugateddiene-based polymer, B′ represents a primary amino group protected witha hydrolyzable protective group, a+b+c=2, a represents 1 to 2, brepresents 0 to 1, and n represents 2 to 20; or (2)

where R⁶ and R¹¹ each represent a divalent aliphatic hydrocarbon grouphaving 1 to 20 carbon atoms, a divalent aromatic hydrocarbon grouphaving 6 to 18 carbon atoms, or a single bond, and may be identical toor different from each other, R⁸ represents a divalent aliphatichydrocarbon group having 1 to 20 carbon atoms or a divalent aromatichydrocarbon group having 6 to 18 carbon atoms, R⁷, R⁹, R¹⁰, R¹², and R¹³each represent a monovalent aliphatic hydrocarbon group having 1 to 20carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 18carbon atoms, and may be identical to or different from one another, A²represents a group for bonding the modifying agent and a conjugateddiene-based polymer by adding to, or substituting for, an active site ofthe conjugated diene-based polymer, B² represents a primary amino groupprotected with a hydrolyzable protective group, B³ represents a linear,branched, alicyclic, or aromatic, monovalent hydrocarbon group having 1to 30 carbon atoms and having a functional group selected from the groupconsisting of an isocyanate group, a thioisocyanate group, an imineresidue, an amide group, a cyclic secondary amino group, an onium saltresidue of a cyclic secondary amine, a non-cyclic secondary amino group,an onium salt residue of a non-cyclic secondary amine, an isocyanuricacid triester residue, a cyclic tertiary amino group, a non-cyclictertiary amino group, a nitrile group, a pyridine residue, an onium saltresidue of a cyclic tertiary amine, and an onium salt residue of anon-cyclic tertiary amine, or a linear, branched, alicyclic, oraromatic, monovalent hydrocarbon group having 1 to 30 carbon atoms whichmay contain at least one kind of heteroatom selected from an oxygenatom, a sulfur atom, and a phosphorus atom, a1+b1+c1=2, a1 represents 1to 2, b1 represents 0 to 1, a2+b2+c2=2, a2, b2, and c2 each represent 0to 2, and p and q each independently represent 1 to
 10. 4. A method ofproducing a modified conjugated diene-based polymer, comprising: amodifying step of causing the modifying agent according to claim 1 toreact with an active site of a conjugated diene-based polymer having theactive site to modify the polymer; and a deprotecting step to beperformed after completion of the modifying step.
 5. The method ofproducing a modified conjugated diene-based polymer according to claim4, comprising a hydrolyzing step between the modifying step and thedeprotecting step, or after the deprotecting step or simultaneously withthe deprotecting step.
 6. The method of producing a modified conjugateddiene-based polymer according to claim 4, wherein 10% or more ofalkoxysilyl groups are converted into silanol groups by hydrolysis. 7.The method of producing a modified conjugated diene-based polymeraccording to claim 4, wherein the conjugated diene-based polymer havingthe active site is obtained by subjecting a conjugated diene compoundalone, or the conjugated diene compound and an aromatic vinyl compound,to anionic polymerization with an organic alkali metal compound as apolymerization initiator.
 8. A modified conjugated diene-based polymerobtained by the production method according to claim
 4. 9. A rubbercomposition, comprising the modified conjugated diene-based polymeraccording to claim
 8. 10. The rubber composition according to claim 9,further comprising a condensation-accelerating agent.
 11. The rubbercomposition according to claim 10, wherein the condensation-acceleratingagent is added at a time of synthesis of the modified conjugateddiene-based polymer and/or at a time of preparation of the rubbercomposition.
 12. The rubber composition according to claim 10, wherein acompounding amount of the condensation-accelerating agent is 0.1 to 10parts by mass based on 100 parts by mass of the rubber component of therubber composition.
 13. The rubber composition according to claim 9,comprising 10 to 200 parts by mass of a reinforcing filler based on 100parts by mass of a rubber component formed of 10 to 100 mass % of themodified conjugated diene-based polymer according to claim 8 and 90 to 0mass % of a diene-based rubber.
 14. A pneumatic tire obtained by usingthe rubber composition according to claim 9.